Presbyopia is the loss of accommodation of the crystalline lens of the human eye that often accompanies aging. This loss of accommodation results in an inability to focus on near distance objects. The standard tools for correcting presbyopia are multifocal ophthalmic lenses. A multifocal lens is a lens that has more than one focal length (i.e., optical power) for correcting focusing problems across a range of distances. Multifocal ophthalmic lenses work by means of a division of the lens's area into regions of different optical powers. Typically, a relatively large area located in the upper portion of the lens corrects for far, distance vision errors, if any. A small area located in the bottom portion of the lens provides additional optical power for correcting near distance vision errors caused by presbyopia. A multifocal lens may also contain a small region located near the middle portion of the lens which provides additional optical power for correcting intermediate distance vision errors.
The transition between the regions of different optical power may be either abrupt, as is the case for bifocal and trifocal lenses, or smooth and continuous, as is the case with Progressive Addition Lenses. Progressive Addition Lenses are a type of multifocal lenses that comprise a gradient of continuously increasing positive dioptric optical power from the beginning of the far distance viewing zone of the lens to the near distance viewing zone in the lower portion of the lens. This progression of optical power generally starts at approximately what is known as the fitting cross or fitting point of the lens and continues until the full add power is realized in the near distance viewing zone and then plateaus. Conventional and state-of-the-art Progressive Addition Lenses utilize a surface topography on one or both exterior surfaces of the lens shaped to create this progression of optical power. Progressive Addition Lenses are known within the optical industry when plural as PALS or when singular, as a PAL. PAL lenses are advantageous over traditional bifocal and trifocal lenses in that they can provide a user with a lineless, cosmetically pleasing multifocal lens with continuous vision correction when focusing on objects at a far distance to objects at a near distance or vice versa.
While PALs are now widely accepted and in vogue within the USA and throughout the world as a correction for presbyopia, they also have serious vision compromises. These compromises include but are not limited to unwanted astigmatism, distortion, and perceptual blur. These vision compromises may affect a user's horizontal viewing width, which is the width of the visual field that can be seen clearly as a user looks from side to side while focused at a given distance. Thus, PAL lenses may have a narrow horizontal viewing width when focusing at an intermediate distance, which can make viewing a large section of a computer screen difficult. Similarly, PAL lenses may have a narrow horizontal viewing width when focusing at a neat distance, which can make viewing the complete page of a book or newspaper difficult. Far distance vision may be similarly affected. PAL lenses may also present a difficulty to a wearer when playing sports due to the distortion of the lenses. Additionally, because the optical add power is placed in the bottom region of the PAL lens, the wearer must tilt his or her head back to make use of this region when viewing an object above his or her head which is located at a near or intermediate distance. Contrastingly, when a wearer is descending stairs and assumes a downward glance, a near distance focus is provided by the lens instead of the far distance focus necessary to see one's feet and the stairs clearly. Thus, the wearer's feet will be out of focus and appear blurred. In addition to these limitations, many wearers of PALs experience an unpleasant effect known as visual motion (often referred to as “swim”) due to the unbalanced distortion that exists in each of the lenses. In fact, many people refuse to wear such lenses because of this effect.
When considering the near optical power needs of a presbyopic individual, the amount of near optical power required is directly related to the amount of accommodative amplitude (near distance focusing ability) the individual has left in his or eyes. Generally, as an individual ages the amount of accommodative amplitude decreases. Accommodative amplitude may also decrease for various health reasons. Therefore, as one ages and becomes more presbyopic, the optical power needed to correct one's ability to focus at a near viewing distance and an intermediate viewing distance becomes stronger in terms of the needed dioptric optical add power. By way of example only, an individual 45 years old may need +1.00 diopters of near viewing distance optical power to see clearly at a near point distance, while an individual 80 years old may need +2.75 diopters to +3.00 diopters of near viewing distance optical power to see clearly at the same near point distance. Because the degree of vision compromises in PAL lenses increases with dioptric optical add power, a more highly presbyopic individual will be subject to greater vision compromises. In the example above, the individual who is 45 years of age will have a lower level of distortion associated with his or her lenses than the individual who is 80 years of age. As is readily apparent, this is the complete opposite of what is needed given the quality of life issues associated with being elderly, such as frailty or loss of dexterity. Prescription multifocal lenses that add compromises to vision function and inhibit safety are in sharp contrast to lenses that make lives easier, safer, and less complex.
By way of example only, a conventional PAL with a +1.00D near optical power may have approximately +1.00D or less of unwanted astigmatism. However, a conventional PAL with a +2.50D near optical power may have approximately +2.75D or more of unwanted astigmatism while a conventional PAL with a +0.3.25D near point optical power may have approximately +3.75D or more of unwanted astigmatism. Thus, as a PAL's near distance add power increases (for example, a +2.50D PAL compared to a +1.00D PAL), the unwanted astigmatism found within the PAL increases at a greater than linear rate with respect to the near distance add power.
More recently, a double-sided PAL has been developed which has a progressive addition surface topography placed on each side of the lens. The two progressive addition surfaces are aligned and rotated relative to one another to not only give the appropriate total additive near distance add power required, but also to have the unwanted astigmatism created by the PAL on one surface of the lens counteract some of the unwanted astigmatism created by the PAL on the other, surface of the lens. Even though this design somewhat reduces the unwanted astigmatism and distortion for a given near distance add power as compared to traditional PAL lenses, the level of unwanted astigmatism, distortion and other vision compromises listed above still causes serious vision problems for the wearer.
Therefore, there is a pressing need to provide a spectacle lens and/or eyewear system that satisfies the vanity needs of presbyopic individuals and at the same time corrects their presbyopia in a manner that reduces distortion and blur, widens the horizontal viewing width, allows for improved safety, and allows for improved visual ability when playing sports, working on a computer, and reading a book or newspaper.